Uniquely resonant coil



Sept. 22, 1925.

. A. PRESS UNIQUELY RESONANT COIL Filed Jan, 11, .1922 2 sheets-Sheet 1 W'ZWm/e A. PRESS UNIQU'ELY aa sonm con.

mm .m'. 11, 1922' 2 sum-sum 2 r0 en ero76r Patented Sept. 22, 1925.

A UNITED STATES:

PATENT. OFFICE.

ABnAnAM-rREss, or wasnmeroltnrsrarcr or COLUMBIA.

UNIQUELY nnsom n'r' corn.

Application filed January 11, 1922. Serial No. 528,581.

To all whom it may concern:

Be it known that I, ABRAHAM Pnnss, citizen of the United States, residing at Wash ington, District of Columbia, have invented certain new and useful Improvements in Uniquely Resonant Coils,fof which the following is a specification. I

This invention relates to tuning coils such as areused in connection with wireless circuits, or the like, and has special reference to the coupling coils of antennae.

Heretofore in the art it had been well known that sharpness of tuning'could be obtained, to a degree, ,with the usual forms. of constructions of coupling or loading coils or the like. It is a fact nevertheless that where the impressed source of potential included undesired harmonics, that such harmonics, as for example the fifth in an are set, could not be tuned out or eliminated when merely tuning for the fundamental.

The present invention has for one of its objects the disclosure of a method and means for increasing the sharpness of tuning -of loading coils, inductances or the like, for any predetermined frequency. Thus in particular antennae wherein an adjustable loading or coupling coil is used, with adjustable contactors or the like, it is possible to adjust sharply for the antinodal (or nodal) points normally set up.

Having determined the necessary conditions for the clear manifestation of nodal and antinodal points, it appears that there are innumerable ways of satisfying the above conditions, .some of which however are naturally much more practical than the remainder. Manifcstly the invention in its broadest aspect includes all manner of additions to well. known types of coils, or even changes from the usual constructions. A novel nethod is also disclosed for arriving at constructions whichflwill satisfy the necessary conditions for sharpness of resonance.

'lVith a view to a better understanding of the principles involved in' this invention, the following theoretical development is made part of this specification in which Fig. 1 represents the usual type of simple antenna connection.

Fig. 2 corresponds to Fig. 1 and schematically illustrates the stationarv vrave effects set up in the coupling coil, wherein the antinodal current on the coil merges with the antinodal stationary wave of current on the aerial,

close to the coupling coil as possible.

Fig. 3 schematically represents the electrostatic field set up about a coupling coil.

4 corresponds to Fig. 3 but illustrates the typeof magnetic field set up in the coil.

Fig. 5 illustrates a method of determining the self induction distribution along a coil or helix. s

Fig. 6 illustrates a modified type of coil shown in Fig. 5.

Fig. 7 illustrates a device for determining the electrostatic distribution about a coil of the type shown in Fig. 5.

Fig, 8 represents a type of uniquely resonant'coil contemplated by this invention.

Fig. 9 illustrates the method of using an arc generator in connection with a uniquely resonant coil.

Fi 10 is a modification'of Fig. 9.

11' shows the use of auniquely resonantcoilin conjunction with an antenna reception circuit.

Figs. 12 and 1?) illustrate the impressed and'reflected waves set up along the coil.

Figs. 13, 13 13illustrate the manner in which dissonance is produced by reflection effects. 1

Fig. 14 illustrates an end connection device for uniquely resonant coils.

Figs. 15-17 illustrate alternatives to the embodiment illustrated in Fig. 14:.

It to remembered that the antenna and ground adjustments (5,, a, to a coupling coil secondary Z are ordinarily made in such a In anner that preferably the maximum amount of antenna current i is indicated in the hot wire instrument or the like A inserted as In view of the fact that the exciting circuit or coil 2 being of an alternating current character, it necessarily follows that it practically determines the position of a nodal point 11. in the secondary such that on the one side ofthis point the potential is plus and the other side minus, and vice versa. In stationary wave theory therefore the distribution of potential 6 and current i must be substantially as indicated in Figure 2. An antin'ode of current should therefore occur at a as well as at a, and a On the other hand potential nodes occur at the points just mentioned. Naturally all such distributions are masked to a great extent by proximity of the earth to the coupling coil, and also due to the fact that to some extent at least progressive waves are set up in the coupling coil, contributing their quota to the aggregate radiation. The stationary wave theory of a helix with respect to earth has already been given by applicant (see paper on lVave velocity along coils in the Electrician, London, June 7, 1918). Professor Fleming had already experimentally determined that the wave velocity along coils did not accord with the velocity of light, but in his particular case was only 1/150th of the same. The same sort of slow wave condition applies to the case of a free helix or coupling coil raised as far as possible from the electrostatic influence of the earths surface. The stationary distribution on such free coils has been very effectively demonstrated by Professor J. S. Townsend of Oxford University, in the Journal of the 1. E. 18., London, for July, 1921. If then a free coil, preferably, canbe made to resonate sharply for a fundamental frequency, by means of the present. invention, it will mean that any parasitic harmonic effect will be eliminated provided the adjustments a (5 are made in the first place for such predetermined frequency. In other words, as a distinct feature of the invention resonance or wave coils of a fixed predetermined type for a given single frequency or wave length are to be introduced into the antenna circuit with a view to being sharply dissonant for any other disturbing frequency or wave length.

In order to determine the underlying principle of such uniquely resonant coils it is necessary to consider the differential equations of condition for the more general case, where both the self induction (inductivity) L,., as well as the capacity (1,, per unit of lengths are functions, distributedly, of the coil coordinate as measured along the axis, from the geometric center of the coil. It is to be noted (see Figure 3) that the capacity per unit of length C for example, for a coil element (annulus) of width (Z02, will be much smaller for the distance I), from the geometric center than for the distance 5 Such capacity function O is by no means dependent on any frequency magnitude of the impressed EM. F. but depends whollyon the steady (DC) state potential function V e =o, which Laplacian method isthe one in accord with Maxwells electromagnetic theory. The inductivity function L,- is determined by a similar DC condition. From inspection of Figure 3 it is clear that contrary'to the case of the vertical grounded antenna already treated by applicant in the proceedings of the LEE. of December 1918, both functions C and L diminish together in magnitude. Whereas however the electrostatic displacement flux is one-way, both for the interior'of the coil as well as in the exterior (see arrows Figure in the case of the magnetic flux the tubes would be in one direction Within the coil, but in the opposite direction outde' (la FFTZZ 1 an U x (if (it The above general equations have been developed by applicant in the Institute of Radio Engineers paper for November, 1920, when dealing with the Besse-lls antenna problem. Separating out the voltage from the current function we have d e d 1 (16 (Z26 (Z 71 (Z 1 (Z'1l d i It is the above type of equations that needs to be solved for the problem at hand.

In view of the fact that both the L and C diminish together for increasing values of the argument 0:, applicant conceived the idea of so coordinating the two functions that we have substantially the conditions where the L and C are constants, and the function e is the general type of condition which is the crowning feature of the present invention.

To an extent it must be stated that if the antenna coupling (or loading) coils are wound with suitable dielectric material between turns, that then the electrostatic con dition can be made to approximate at least to the condition It should be borne in mind that the essential condition is rather one of kind than of equal magnitude. Thus it appears that a straight uniform helix Wound with suitable insulated wire, or one wound with bare wire upon a dielectric hollow mandrel will ap n-oximatr-ly meet the above required conditions (3). Howeventhis type of coupling or loading coil construction appears to have been determined previously by Colonel Mauborgne and Captain Hill of the Signal Corps, U. S. Army to give strangely enough, a sharply resonant combination for the usual antenna constructions. However, such prior invention acknowledgment of which is herewith made. had been rather in the nature of experimental than mathematical discovery. Thus the present disclosure though including lUO the earlier Mauborgne Hill Wave coil as a special case also includescoils and combinations not contemplated by them, since the governing conditions of construction are according to thepresent invention the simul-- with a similar equation ini'instead of 6.

Now it transpires-that the solution of (4), for stationary waves for sustained oscillations of periodicity 1(21r).p:f has been originally'determined by applicant to be of a form where the corresponding function for current would be of the form e Asin f(w) sin pt standard Maxwellian methods for the determination of the line constants L and C whether for long or short waves. The necessary and sufficientcondition for determining the unknown function will be found to be r so that if (x) is known H) and the solutions (6) and (7) are known for any particular case. It should be added that the solutions (6) and (7 require that we have LCp ZI f i 1 I whencef=m (9) throughout the coil then will it belfound that the coil is uniquely resonant to the fre quency f given by equation For any other frequency the coil will actually be dis sonant. The problem then is, so to arrange the elements of the coil that the proportionality (10) obtainssubstantially throughout In order to carry out the above condition the'following method can be employed An arbitrary helix devoid of insulation such as the curved helix (Figure 5) isfirst excited with a definite amount of current by means of a DC source B by means of a switch S and then explored by means of an exploring loop EL connected to a ballastic ga-lvanometer G. duction function can be determined.

If now a template made up of four sections 5, 5, 6, 6; is made up to practically simulate the cross section of the coil, with the one portion 5, 5 connected together by means of suitable leads 5, 5 and 6', 6 to a suitable source of low tension alternating current A. C. it is possible to map out the lines of electrostatic flux both within and without the coil. This is accomplished in the following manner. The template is im mersed in a flat dish I) in which: latter is placed some electrolite such as dilute sulphuric acid. Then by a point by point method the flux lines of alternating current flow can be suitably mapped by means of a telephone 17. Thus to determine the point along the flux line curve, corresponding to the point 79, an exploring needle?" similar to that of 7 placed at the point p, is used. It will be found that only at point such as was against the points 79, and 72, will the maximum sound he heard in the telephone. In this manner having determined the tubes of flux, a graded type of dielectric for the individual tubes mapped out can be made use of in order to give the requisite amount of electrostatic displacement for the elc ments Am (approximations to (Z00) so that the function is obtained. Instead of the coil (Figure 5) for example, a coil such as (Figure 6) could be used. Obviously the distinction between the above more nearly theoretical coil, according to the present theory, and the Mauborgne-Hill straight cylindrical wave coil is. that insulation is preferably 7 employed both outside and within the coil.

On the other hand, instead of employing an electrostatic correction alone,v a combined magnetic method can be employed. Thus two shields (curved orotherwise) of In this way the self -in-- magnetic material (powdered if desired) can be employed, in order to limit both the electrostatic induction lines as well as those of magnetic induction. In the case of high frequency currents, clearly the shields internal and external, may be split tubes (curved or otherwise) of sheet metal such as copper. Then in view of eddy current shielding the magnetic flux will not be able to penetrate the copper to any great extent provided very high frequency currents are employed.

Such a type of coil is indicated in Figure 8,where the coil. has placed within it a suitably shaped inner shield, in the diagram flared inwardly toward the ends, and an external split shield 9 in the diagram flared outwardly toward the ends. The spacings (1) cos [q5 (m) pt] cos (ta: (2) cos [qf (:t) +pt]=cos (155E \Vhen the two waves meet in proper phase relationship we have by superposition cos ((1533 pt) +cos (q5a;+ pt) 2 cos qbrt cos pt It istlie right hand term which represents the resultant stationary wave. Thus it is important to avoid disturbing dead ends.

Should it transpire that the end of the coil does not exactly correspond to an antinodal point as is indicated in Figure 12 (condition m: where equalsthe wave length) we will have instead of a reflected wave such as that indicated in Figure 12*, a reflected wave as indicated in Figure 13 which latter condition tends to set up a further wave 13 which latter by the time it reaches the end of the coil may be progressively out of phase with the original wave Figure 13, and thus set up a complexity of waves tending to produce dissonance which dissonance will be most complete when m is an incommensurable part of unity.

To bring out this feature, in the case of uniquely resonant coils, we note that the function 1 -sin e 13 of the one shield from the other can be so proportioned as to satisfy the required condition (10) above. Be it observed that by means of reticulated shields the function (m) can indeed be made to accord only for frequencies substantially above a predetermined amount when the skin efl'ect begins to count for the higher frequencies.

The conditions tending to set up disso nance are very important, and lead to constructions serving to produce sharper resonance than has heretofore been possible. In so far as stationary waves can be conceived as set up by oppositely directed progressive waves, one of which is the inipressed forward wave and the other the opposed reflected wave from the end of the coil, we have the following:

embodiment curved tubing which can be slipped over the free ends of the coil 1 for adjusting purposes. Still another method can be employed comprising the use of contacting strip instead of tubing. A still further method can be employed which comprises the use of reticulated material or caps e0, ec covering the ends of the coils, which caps may or may not .be connected to earth, and aerial of the antenna system. It should be pointed out however that it is not necessary to have both ends capped to obtain the desired result, nor is it necessary to provide the shielding arrangement at the ends of the coil. Thus an adjustable sliding sleeve of a split type can be employed about the center of the coil as idicated in Figure 16. An equivalent method is indicated in Figure 17 where the two helices are provided with an adjustable central sliding or capacitance connection or the like.

I claim- 1. In combination with a source of alternating electromotive force, an open ended helix comprising a shielding means, said shielding means extending substantially a half stationary wave length of said helix for the frequency of said electromotive force.

2. An open ended helix comprising a conductive shielding means internal and external to said helix.

3. A method of making up uniquely resonant coils, comprising the step of determining the coefficient of self induction distribution, and then modifying the coeflicient of capacity distribution, to give a substantially linear relationship between said coefiicients.

4. In combination With an antenna, an arc source of electro-motive force, a uniquely resonant coupling coil, and means for eliminating the are harmonics by adjusting said coupling coil for the uniquely resonant wave length corresponding to the fundamental of said are source.

5. In combination with an electric source of high frequency, a helix, means for producing a uniquely resonant characteristic in said helix, said means comprising a device for adjusting the phase of the reflected Waves to produce stationary Waves on said helix.

6. In combination with an open ended helix, means for positioning the reflecting open end effects of said helix.

7. An open ended helix comprising in combination, an adjustable means for varying the end spire length of said helix.

8. A uniquely resonant helix, comprising in combination, means for adjusting the effective end spire length of said helix.

9. A uniquely resonant coil comprising in combination a means for adjusting the effective dead end spire length of said coil.

In testimony whereof I have afiixed my signature.

ABRAHAM PRESS. 

